1. Field of the Invention
This invention relates to fixing baths for the removal of silver halide from unexposed portions of black and white photographic elements and to a method of fixing unexposed portions of black and white elements. More particularly, this invention relates to an improvement in fixing baths for black and white photographic elements whereby stain problems are eliminated and thiosulfate is removed from the fixed element.
2. Description of Related Art
Japanese Kokai No. Sho 49(1974) 40943 discloses a bleach fixing composition containing an iron(III) complex, a water-soluble silver halide fixing agent and an imidazole compound wherein the imidazole compound is used in extremely large quantities (the lowest amount being 40 g/L) with respect to the total quantity of the liquid fixing bath. The purpose for the imidazole compound is to prevent the precipitation of the iron(II) complex salt when various chemicals are added to the solution.
With the advent of automatic processors for the development of photographic elements and the printing of photographic images, the requirements for the various baths utilized in these procedures has become more stringent. Since these devices are generally continuous type devices wherein the element is introduced at one point and extracted from another, speed is an important factor. Secondly, the processors themselves must be capable of developing and printing photographic films and papers of all of the various manufacturers. Thus, the various solutions used in the different tanks of the processor must be capable of bringing about the desired result regardless of the origin of the product introduced, said product being the photographic imaging element of any of the commercially available manufacturerers. Thus, in the practice of developing photographic elements, whether it is by a manual technique or in an automatic processor, the solutions employed must be uniformly applicable to all elements without introducing unwanted disadvantageous characteristics to any particular one. Further, the processor and the various solutions used therein must be capable of achieving the desired result for example, the fixer must be capable of removing the silver halide from unexposed regions of the element in a rapid manner without adversely affecting either the appearance or archival stability of the resulting product.
While the primary function of the fixing bath is to remove the unexposed silver halide salt, it is necessary that the thiosulfate ion which is incorporated in the fixing bath to accomplish this purpose, also be removed as rapidly and completely as possible. Retained thiosulfate ion in the element is a factor in shortening archival life. Thus, it is a requirement that this material be thoroughly removed during the processing thereof.
Another requirement in the processing of black and white film is that any of the dyes employed in the preparation of the film, whether they be sensitizing dyes, antihalation dyes which are generally incorporated in the pelloid layer of the film, or the like, not interfere with the appearance or performance of the product. With the advent of high speed automatic processors, this becomes a more stringent requirement because high solution concentrations are employed and less time is available for each cycle of the processor. Should such dyes remain in the film, their presence is manifest by what is commonly referred to as "dye stain". Residual sensitizing dye stain is often more severe where the silver halide grains of the element have a large surface area. This is a discoloration of the processed film and can be clearly demonstrated by fixing an unexposed film and observing the result thereof.
In addition, any alteration in the ingredients employed in the processing of black and white film which will permit fast cycles through the processing bath is desirable.